ENH: Add hpi_colors and hpi_labels for clear visualization

[drona-gyawali]

Reference issue (if any)

Fixes #13485.

What does this implement/fix?

• Automatically uses official MEGIN cable colors (1=red, 2=blue, 3=green, 4=yellow, 5=magenta, 6=cyan)
• Optional hpi_labels=True shows coil ident as 3D text
• Fully user-configurable (list/dict/single color)
• Added test coverage

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